The present invention relates to a device for locking and unlocking a door of an object, particularly of a motor vehicle, having a transmitter unit disposed on the object and a response device transponder assigned to a user.
A device for keyless locking and unlocking of a door is described in xe2x80x9cKeyless Entry System With Radio Card Transponderxe2x80x9d, Motoki Hirano et al, IEEE Transactions on Industrial Electronics, vol. 35, 1988, pp. 208 through 216. A locked door of a motor vehicle is unlocked as soon as a user who is carrying a transponder enters into the interrogation field of a transmitter unit located in the region of the door, triggers the interrogation, and the transmitter unit has recognized the code of the transponder as correct with the aid of an appropriate evaluation unit. A problem involved with such a device is that the vehicle door can be opened from the outside when the driver having the transponder is in the passenger compartment of the vehicle, although, such as when waiting in his vehicle in a parking lot, he would like to keep the door locked.
For example, if the transmitter unit is accommodated in an outside mirror, where the transmission radiation lobe normally does not reach the passenger compartment, then an attacker can pivot the outside mirror in order to direct the transmission lobe toward the transponder and unlock the door.
An object of the present invention is to provide a device with which an unwanted unlocking of the door can be reliably prevented.
According to the present invention in response to alignment of the transmission lobe with the interior of the object, the range of the field of the transmission lobe formed by the transmitter unit or of the signals emitted by the transponder can be reduced or disturbed by a switching device, so that a transponder located in the passenger area of the interior cannot be queried.
Because the range of the field of the transmission lobe or of the signals emitted by the transponder is reduced or disturbed, an interrogation of the transponder located in the passenger compartment of the motor vehicle is prevented. The door remains locked as long as the user desires.
A simple design of the device lies in the fact that the transmitter unit is disposed in an outside mirror of the motor vehicle, and that the switching device has sensor elements which function in response to an adjustment of the outside mirror in such a way that the transmission lobe is directed into the passenger compartment. With the aid of the switching device which, for example, can also be constructed electronically, the range of the field is reduced, e.g., to a few cm, so that the transponder of the occupant is not reached, or an interference source is switched on so that the transponder likewise cannot be queried.
Furthermore, in one advantageous embodiment, the sensor elements are contact elements arranged in the hinge of the outside mirror.
For example, if the transmitter unit is built into the door, then the field can be switched to the short range or the interference source can be switched on because the switching device has an operating device located in the passenger compartment which can be actuated by the user. Besides the arrangement in the mirror, suitable locations for mounting the transmitter unit are in the door or its edging.
The interrogation of the transponder in the passenger compartment can also be highly effectively prevented by arranging an interference source, whose radiating frequency corresponds to that of the transmission device, in the passenger compartment in order to disturb the field in the passenger compartment.